1. Field of the Invention
The present invention relates to an X-ray computed tomography apparatus and image processing apparatus which generate a plurality of volume data sets with different scan times for the same scan area of an object to be examined.
2. Description of the Related Art
In an X-ray computed tomography apparatus, a technique called a 4DCT scan is available to generate a plurality of volume data sets with different scan times for the same scan area. Recently, this 4DCT scan can superimpose a blood vessel image and a functional image for a blood flow (perfusion). This superimposition processing is useful for image diagnosis. A blood vessel image concerns a time (e.g., a time near a peak of a TDC) at which a blood vessel is imaged most clearly by CT angiography (CTA). A functional image is calculated on the basis of a plurality of volume data sets. More specifically, a functional image is generated by calculating an index (e.g., a CBP, CBV, or MTT) indicating the blood flow dynamic state of tissue (e.g., brain tissue) for each voxel and assigning pixels pieces of color information corresponding to the calculated index values (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 2003-190148).
When a blood vessel image is to be generated, since different volume data sets to be processed exhibit different blood flow dynamic states, the user needs to designate optimal positions (or ranges) for blood vessel image generation for all the volume data sets. In addition, when blood vessel image data is generated on the basis of the volume data set, of all the volume data sets, which concern a predetermined period of time, the generated blood vessel image does not contain any information about a blood vessel at which a contrast agent has not arrived within the predetermined period of time. This causes a phenomenon in which the blood vessel is not imaged even after the function is restored.
When function analysis based on TDC (e.g., an algorithm such as the deconvolution method) is to be executed on the basis of a plurality of volume data sets with different scan times, since the amount of data to be processed is large, a problem arises in terms of processing time.